Compact Beamforming Receiver Front End

The present disclosure relates to electronic device design, and in particular to radio-frequency (RF) receivers that perform beamforming using phase shifting.

A beamforming (BF) receiver may apply respective phase shifts to signals from a plurality of antennas (or more generally a plurality of sensors, such as optical or acoustic sensors) in order to produce directional signal reception. Phase shifting a signal having a frequency ω by a phase shift φ may be produced using the trigonometric identity:

sin(ω+φ)=*sin(ω)+*cos(ω)  Equation 1

The phase shifted signal may then be combining with respectively phase shifted signals from other antennas, amplified by an RF variable gain amplifier (VGA), and down converted to an intermediate frequency for further processing.

In BF receivers of the related art, I and Q signals are generated for each antenna as part of the phase shifting process. Generation of these signals may employ electromagnetic (EM) circuits, such as Quadrature Hybrid Couplers (QHCs) and transformers. These EM circuits may be on the same semiconductor die as other electronic circuits in the BF receiver, may be quite large compared to those other circuits, and may be provided for each antenna that the BF receiver supports. As a result, the EM circuits may cause the semiconductor die to become larger, increasing the cost of the BF receiver. Furthermore, the circuitry associated with the EM circuits may consume substantial amounts of power.

Because BF receivers are now a substantial portion of the bill-of-materials cost and power consumption of popular wireless communication devices such as mobile phones, a need exists for reduction of the complexity, area, and power of BF receivers.

Embodiments of the present disclosure relate to circuits and methods for use in a beamforming receiver. More specifically, the circuits and methods relate to performing beamforming by phase shifting and combining a plurality of signals.

In an embodiment, a beamforming front end (BFFE) for a receiver comprises first and second signal chains, an I combiner circuit, a proxy-quadrature (PQ) combiner circuit, and a converter circuit. The first signal chain is configured to receive a first signal, produce a first I signal by amplifying the first signal by a first I gain value, and produce a first PQ signal by amplifying the first signal by a first Q gain value, wherein the first I signal and first PQ signal are mutually in-phase, and wherein the first I gain value and first Q gain value correspond to a first phase shift. The second signal chain is configured to receive a second signal, produce a second I signal by amplifying the second signal by a second I gain value, and produce a second PQ signal by amplifying the second signal by a second Q gain value, wherein the second I signal and second PQ signal are mutually in-phase, and wherein the second I gain value and second Q gain value correspond to a second phase shift. The I combiner circuit is configured to produce a combined I signal by summing respective values of the first and second I signals. The PQ combiner circuit is configured to produce a combined PQ signal by summing respective values of the first and second PQ signals. The converter circuit is configured to produce, based on the combined I signal and combined PQ signal, an output signal corresponding to the first signal phase-shifted by the first phase shift and the second signal phase-shifted by the second phase shift.

In embodiments of the BFFE, the converter circuit comprises a quadrature local oscillator circuit configured to generate an in-phase (I) local oscillator signal and a quadrature (Q) local oscillator signal having a phase different from the I local oscillator signal; an I mixer configured to produce a converted I signal by mixing the I local oscillator signal with the combined I signal; a Q mixer configured to produce a converted Q signal by mixing the Q local oscillator signal with the combined PQ signal; and a combiner circuit configured to produce the output signal by combining the converted I signal and the converted Q signal.

In an embodiment, a method of performing beamforming in a receiver comprises producing a plurality of I signals and a plurality of PQ signals based on a plurality of received signals and a plurality of gain value pairs by, for each received signal and the corresponding gain value pair, producing the corresponding I signal by amplifying that received signal by an I gain value of that gain value pair and producing the corresponding PQ signal by amplifying that received signal by a Q gain value of that gain value pair. The corresponding I signal for each received signal has the same phase as the corresponding PQ signal for that received signal. The method further comprises producing, using the plurality of I signals, a combined I signal having a value corresponding to a sum of values of the plurality of I signals; producing, using the plurality of PQ signals, a combined PQ signal having a value corresponding to a sum of values of the plurality of PQ signals; and producing, using the combined I signal and the combined PQ signal, an output signal corresponding to a sum of the plurality of received signals respectively phase shifted by an amount corresponding to the corresponding gain value pair of the plurality of gain value pairs.

In embodiments of the method, producing the output signal comprises producing an in-phase local oscillator signal and a quadrature local oscillator signal, producing a converted I signal by mixing the in-phase local oscillator signal with the combined I signal, producing a converted Q signal by mixing the quadrature local oscillator signal with the combined PQ signal; and producing the output signal by combining the converted I and Q signals.

Illustrative embodiments of the present disclosure will be described below in more detail with reference to the accompanying drawings. The inventive features may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present claims to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments.

It will be understood that, although the terms “first” and/or “second” may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a first element discussed below could be termed a second element without departing from the teachings of the present disclosure. Similarly, the second element could also be termed the first element.

The drawings are not necessarily to scale and in some instances, proportions may have been exaggerated in order to clearly illustrate features of the embodiments.

Embodiments described herein relate to RF signals received through antennas and processed using antenna chains, but embodiments are not limited thereto. Accordingly, embodiments may relate to electromagnetic, optical, acoustic, or other signals received and processed through appropriate sensors and respective signal chains, wherein the signal chains include features corresponding to features of the antenna chains described herein.

In this disclosure, “electromagnetic (EM) components” refers to electrical components that rely on the interaction of magnetic fields for their operation. Such EM components include inductors, transformers, hybrid couplers, and components comprising transmission lines and/or waveguides wherein the arrangement and dimensions of the transmission lines determines the operation performed by components. Examples of the latter include Wilkinson splitters/combiners, impedance transformers, directional couplers, and the like.

conceptually illustrates the operation of a beamforming front-end (BFFE)of a BF receiver. The BFFEcomprises N signal chains comprising antenna chains-through-, where N is equal to or greater than 2, which are coupled to corresponding antennas-through-. The antenna chains-through-comprise RF low-noise amplifiers (LNAs)-through-and phase shifters-through-, respectively. The BFFEfurther comprises a combinerand an IF converter, the latter comprising a local oscillatorand a mixer. In embodiments, the antenna chains-through-, combiner, and IF converterare all components in the same semiconductor die, which in some embodiments may also include other circuits of the BF receiver.

Each of the antennas-through-receives a radio signal from a same source. The relative phases of the radio signal as received varies according to the direction from which the radio signal arrives and the physical configuration of the antennas.

The respective signals are amplified by RF LNAs-through-, phase shifted according to the desired reception pattern for the BFFEby the phase shifters-through-, and then combined by the combiner. The resulting RF signal is then mixed with the output of the local oscillatorby the mixerand then low-pass filtered to produce the intermediate frequency (IF) signal IFout. In an illustrative example, when the RF signal has a frequency of about 28 GHz and the frequency of the local oscillatoris 19.5 GHZ, the IF signal IFout will have a frequency of about 8.5 GHz.

To illustrate operation of the invention, an unmodulated radio signal is analyzed. For an unmodulated radio signal, the IF signal IFout would correspond to:

While embodiments effectively perform the operations performed by the elements of the BFFEillustrated in, embodiments may split-up and re-arrange portions of the operations as described below. In particular, embodiments may not produce true (that is, actually phase-shifted) quadrature signals in the antenna chains, and may thereby eliminate the need for the large EM circuits typically used to generate quadrature signals in the antenna chains. In BF receivers that support a large number of antennas, this may produce substantial die area savings.

illustrates a front-end of a BFFEaccording to an embodiment. The BFFE comprises a plurality of antenna chains-through-, a combiner, and an IF converter. In the BFFE, performance of the phase-shifting of the radio signals is distributed across the antenna chains-through-, the combiner, and the IF converterso that quadrature signals do not need to be generated in the antenna chains-through-

Instead, the antenna chains-through-respectively generate I signals Ithrough In and proxy quadrature (PQ) signals PQthrough PQn. The I signals Ithrough In are respectively produced by multiplying the radio signals by I gain (IG) values IGthrough IGn, and the PQ signals PQthrough PQn are produced by multiplying the radio signals by Q gain (QG) values QGthrough QGn, but unlike in the Q signals in antenna chains of the related arts, the PQ signals PQthrough PQn are not phase-shifted; that is, they are in-phase with the I signals Ithrough In.

The combinerindependently combines the I signals Ithrough In to produce a combined I signal CI and combines the PQ signals PQthrough PQn to produce a combined I signal CPQ. The combined I signal CI and combined PQ signal CPQ correspond to:

The IF converterperforms both the phase-shifting and the down conversion of the combined I signal CI and combined PQ signal CPQ. Specifically, the IF convertermixes the combined I signal CI with an in-phase local oscillator (LO) signal LO_I generated from the local oscillator output LO of the local oscillator, and mixes the combined PQ signal CPQ with a quadrature LO signal LO_Q generated from the local oscillator output LO. The mixer outputs are then combined to produce the IF signal IFout:

In more detail, for each antenna chain-in the antenna chains-through-, the antenna chain-receives a radio signal from antenna-. The radio signal is amplified by RF low-noise amplifier (LNA)-. In embodiments, the RF LNA-through-each include a degeneration inductor.

In embodiments, the output of the RF LNA-is a balanced signal having a voltage according to the radio signal. In some embodiments, the voltage may be a differential voltage. In embodiments, the outputs of the RF LNAs-are carried by transmission lines.

The output of the RF LNA-is amplified by I-signal variable gain amplifier (VGA)I-x to produce an I signal Ix; the gain of the I-signal VGAI-x is determined according to the I gain signal IGx. The output of the RF LNA-is also amplified by Q-signal VGAQ-x to produce a PQ signal PQx; the gain of the Q-signal VGAQ-x is determined according to the Q gain signal QGx.

In embodiments, the I-signal VGAI-x and the Q-signal VGAQ-x are transconductance amplifiers that respectively output a current corresponding to the product of the value of the output of the RF LNA-and the value of the I gain signal IGx and a current corresponding to the product of the value of the output of the RF LNA-and the value of the Q gain signal QGx.

In embodiments, each of the I signals Ix and the PQ signals PQx is a balanced pair of signals wherein their value corresponds to a difference between the currents of the pair of signals. In embodiments, the I signals Ix and the PQ signals PQx are carried by transmission lines.

Notably, each antenna chain-only requires a single stage of amplification before the circuitry that generates the I and PQ signals used to perform phase shifting. In contrast, because of the need to generate a true quadrature signal in antenna chains of BFFEs of the related arts, the antenna chains of BFFEs of the related arts typically require multiple stages of amplification before the circuitry that generates the quadrature signal.

In the combiner, an I-current combinerI combines the first to nI signals Ithrough In to produce the combined I signal CI, and a PQ-current combinerPQ combines the first to nPQ signals Pthrough Pn to produce the combined PQ signal CPQ. A value of combined I signal CI may correspond to a sum of values of the first to nI signals Ithrough In, and a value of combined PQ signal CPQ may correspond to a sum of values of the first to nPQ signals PQthrough PQn.

Each of the I-current combinerI and the PQ-current combinerPQ may comprise a RF current combiner as known in the related arts, such as a current-mode Wilkinson combiner. In embodiments, each of the combined I signal CI and the combined PQ signal CPQ is a balanced pair of signals wherein a value corresponds to a difference between the currents of the pair of signals.

The IF converterperforms both the phase shifting and down conversion for the received signals, as generally described previously. In detail, the local oscillatorgenerates a local oscillator output LO, and a quadrature generatorgenerates an in-phase (I) local oscillator signal LO_I and a quadrature (Q) local oscillator signal LO_Q.

In embodiments, the quadrature generatoruse an electromagnetic component, such as quadrature hybrid coupler, to generate the Q local oscillator signal.

In other embodiments, the quadrature generatormay use resistor-capacitor (RC) filters, capacitor-resistor (CR) filters, or both to generate the Q local oscillator signal; while RC/CR-filter based quadrature generation is lossy and inefficient (and may therefore be unsuitable for use earlier in the BFFE, such as in the antenna chains), such quadrature generators typically are substantially smaller than electromagnetic quadrature generators.

The I local oscillator signal LO_I is mixed with the combined I signal CI by the I mixerI to produce a down-converted combined I signal DCI. The Q local oscillator signal LO_Q is mixed with the combined QP signal CQP by the Q mixerQ to produce a down-converted combined Q signal DCQ. The I mixerI and the Q mixerQ may comprise a suitable mixer known in the related arts.

The down-converted combined I signal DCI and the down-converted combined Q signal DCQ are combined by the IF combiner. The IF combinermay comprise a current combiner based on load transformer. As demonstrated by the analysis shown in Equations 1-8, above, the output of the IF combineris an IF signal IFout corresponding to the beamformed and down-converted received radio signal.

illustrates a portion of a BFFEof a beamforming receiver according to an embodiment. The BFFEcorresponds to the BFFEofwith additional elements. Except as detailed below, elements of the BFFEhaving reference characters of the form 3xx or 3xx-x respectively correspond to elements of the BFFEhaving reference characters of the form 2xx or 2xx-x, and accordingly a repetitive description of such elements is omitted in the interest of brevity.

Relative to the BFFEof, the BFFEadds first and second matching networks (MNs)-and-and first and second interstage transformers-and-to the first and second antenna chains-and-.

The MNs-and-operate to match the impedance of the antennas-and-to the input impedances of the RF LNAs-and-, respectively. The MNs-and-may each include EM components.

The interstage transformers-and-operate to match the output impedances of the RF LNAs-and-to the input impedances of the corresponding I-signal VGAs-and-and Q-signal VGAQ-x andQ-, to convert the outputs of the RF LNAs-and-to balanced outputs when the RF LNAs-and-have unbalanced outputs, or a combination thereof. The interstage transformers-and-may each include EM components.

Again relative to the BFFE, the BFFEadds I-side VGAI, I-side inter-stage transformerI, Q-side VGAPQ, and Q-side inter-stage transformerPQ to the combiner. A person of ordinary skill in the art would understand the purposes and operation of these additional components. These extra VGAs help to improve the noise figure of the chain and the total maximum gain of the receiver chain. Each of the I-side inter-stage transformerI and the Q-side inter-stage transformerPQ include EM components.

Also in the combiner, the I-current combinerand the PQ-current combinerPQ are each disclosed as also performing the role of matching networks.